The invention relates to improvements in torque transmitting apparatus in general, and more particularly to improvements in torque transmitting apparatus which employ hydrokinetic torque converters. Still more particularly, the invention relates to improvements in torque transmitting apparatus of the type wherein a hydrokinetic torque converter cooperates with or embodies a lockup clutch, also called bypass clutch.
It is known to utilize a hydrokinetic torque converter in the power train between the engine and the transmission in a motor vehicle. As a rule, the torque converter comprises a housing which defines a fluid-filled chamber and receives torque from the output element of the engine. The housing drives a pump which can transmit torque to the input element of the transmission by way of a turbine in the chamber of the housing. A stator can be interposed between the pump and the turbine as seen in the axial direction of the torque converter. The housing of the torque converter can accommodate a lockup clutch having a piston which is movable in the axial direction of the torque converter in response to the establishment of necessary pressure differential between a first compartment of the chamber at one side and a second compartment of the chamber at the other side of the piston. When the lockup clutch is engaged, it can transmit torque from the housing of the torque converter (i.e., from the output element of the engine) directly to the turbine in the chamber of the housing and hence directly to the input element of the transmission.
Torque transmitting apparatus of the above outlined character are disclosed, for example, in U.S. Pat. No. 4,618,041 (granted Oct. 21, 1986 to Sotoyama et al. for xe2x80x9cLockup control system for a torque converter for an automatic transmissionxe2x80x9d), in U.S. Pat. No. 4,619,350 (granted Oct. 28, 1986 to Maezono et al. for xe2x80x9cClutch operation control system for fluid torque converter of vehicular transmissionxe2x80x9d) and in U.S. Pat. No. 4,640,395 (granted Feb. 3, 1987 to Murasugi et al. for xe2x80x9cSlip control mechanism for friction clutch in torque converter of automatic power transmissionxe2x80x9d). The disclosures of the above enumerated patents are incorporated herein by reference.
A drawback of heretofore known torque transmitting apparatus employing hydrokinetic torque converters and lockup clutches is that their operation is not entirely satisfactory under certain circumstances when such apparatus are in actual use, e.g., in the power trains between the engines and the transmissions of motor vehicles. For example, it is often desirable or plain necessary to disengage the lockup clutch, at least for a certain interval of time, during certain stages of operation of the motor vehicle. Such situation can develop, for example, when the temperature of surrounding air is relatively low or very low. The reason is that the hydraulic fluid which is utilized to fill the chamber defined by the housing of the torque converter is normally oil and the viscosity of such fluid increases in response to decreasing temperature. The pumping device which is utilized in conventional torque transmitting apparatus of the above outlined character is incapable of conveying the high-viscosity fluid at a required rate so that the pressure of fluid is too low or cannot be maintained at a desired value, namely at a value which is necessary to ensure that the lockup clutch remains disengaged or that the lockup clutch is disengaged to a desired degree. Such disengagement or partial disengagement of the lockup clutch is ensured if the pressure in one of the aforementioned compartments is maintained at or above a certain value. Many torque transmitting apparatus cannot ensure predictable disengagement or partial disengagement of the lockup clutch if the temperature of the surrounding atmosphere is close to or below 0xc2x0 C.
Additional serious problems can arise when the transmission receiving torque from a standard torque converter is shifted in reverse gear. The reason is that, in many (actually in most) instances, the modulation pressure (namely the pressure which is necessary for proper operation of the gear transmission) increases with simultaneous drop of fluid pressure in the torque converter. This entails undesirable (at least partial) engagement of the lockup clutch. The reason for such at least partial engagement of the lockup clutch under the above outlined circumstances is the development of a force attributable to fluid pressure and arising as an integral effect of variations of fluid pressure at the opposite sides of the piston forming part of the lockup clutch. The variations of fluid pressure at opposite sides of the piston develop primarily as a result of the kinematic and/or dynamic relationships of fluid elements, namely essentially in dependency on their average peripheral speed and hence in dependency on the rotational speed of the parts (such as the housing and the turbine of the torque converter and the piston of the lockup clutch) which flank the aforementioned compartments of the chamber in the housing of the torque converter. Accordingly, the operation of the torque transmitting apparatus is dependent upon the RPM of the pump and turbine of the torque converter and upon the RPM of the piston of the lockup clutch. Reference may be had, for example, to U.S. Pat. No. 3,213,983 (granted Oct. 26, 1965 to Smirl et al. for xe2x80x9cFluid actuated transmission devicexe2x80x9d) which discusses the development and the effects of such forces and pressures. The disclosure of the patent to Smirl et al. is incorporated herein by reference.
An additional drawback of heretofore known torque transmitting apparatus which embody a hydrokinetic torque converter and a lockup clutch is that they are complex and expensive.
An object of the invention is to provide a torque transmitting apparatus which embodies a hydrokinetic torque converter and a lockup clutch and is constructed and assembled in such a way that its operation is satisfactory (or at least more satisfactory than that of heretofore known apparatus) under all circumstances which arise in actual use of such apparatus.
Another object of the invention is to provide a relatively simple, compact and inexpensive torque transmitting apparatus which can be utilized as a superior substitute for heretofore known apparatus employing a hydrokinetic torque converter and a lockup clutch.
A further object of the invention is to provide a novel and improved power train which employs a torque transmitting apparatus of the above outlined character.
An additional object of the invention is to provide a motor vehicle which embodies the improved torque transmitting apparatus.
Still another object of the invention is to provide a novel and improved lockup clutch which can be utilized in the above outlined torque transmitting apparatus.
A further object of the invention is to provide a novel and improved combination of a lockup clutch or bypass clutch and a hydrokinetic torque converter.
Another object of the invention is to provide a torque transmitting apparatus which can operate in a desired manner irrespective of pronounced variations of a number of different parameters such as the RPM of the housing of the torque converter, the temperature of the fluid in the housing of the torque converter and/or the viscosity of such fluid.
One feature of the present invention resides in the provision of a torque transmitting apparatus which comprises a hydrokinetic torque converter having a fluid-containing chamber and including a pump rotatable about a predetermined axis at a variable RPM by a rotary output element (e.g., a camshaft or a crankshaft) of a prime mover (such as the combustion engine or another engine of a motor vehicle). The torque converter further comprises a turbine which is disposed in the chamber and includes an output member which is rotatable about the predetermined axis (the output member can constitute the input element of an adjustable transmission in the power train between the engine and one or more wheels of the motor vehicle). Still further, the torque converter can comprise a stator which is disposed in the chamber between the pump and the turbine, as seen in the direction of the predetermined axis. The apparatus further comprises a lockup clutch or bypass clutch which is engageable to transmit torque of variable magnitude from the output element of the prime mover to the output member of the turbine and includes a piston movable in the direction of the predetermined axis and dividing the chamber into first and second compartments respectively containing bodies of fluid (e.g., oil) at first and second pressures. The differential between the first and second pressures determines the magnitude of torque being transmitted by the lockup clutch, and the apparatus further comprises at least one valve which is adjustable to establish at least one path for the flow of fluid between the first and second compartments at a rate varying as a function of at least one of a plurality of parameters including the RPM of the output element of the prime mvoer, the temperature of the fluid in the chamber and the viscosity of fluid in the chamber to thus influence the pressure differential and hence the magnitude of torque being transmitted by the clutch. The at least one valve is operative (1) to permit the flow of fluid between the first and second compartments in response to at least one of (1a) a reduction of the RPM to below a predetermined RPM, (1b) a drop of fluid temperature below a predetermined value and (1c) a rise of the viscosity of fluid above a preselected value, and (2) to at least reduce the rate of fluid flow between the first and second compartments in response to at least one of (2a) a rise of the RPM above the predetermined RPM, (2b) a rise of fluid temperature above the predetermined value and (2c) a drop of the viscosity of fluid below the preselected value.
The at least one valve can constitute a slide valve, a rotary valve, a cock or a butterfly valve.
For example, the at least one valve can comprise at least one valving element which is acted upon and is movable by centrifugal force in response to rotation of the output element of the prime mover to thereby vary the rate of fluid flow between the first and second compartments. Such at least one valve can further comprise means (e.g., one or more prestressed coil springs) for yieldably urging the at least one valving element in a direction to increase the rate of fluid flow between the first and second compartments.
The at least one valving element of the at least one valve can be constructed, mounted and operated to move in response to changes of at least one of the parameters including the temperature and the viscosity of the fluid in the chamber to thereby vary the rate of fluid flow between the first and second compartments. The at least one valving element can include or constitute a bimetallic element, and the at least one valve can constitute a thermostatic valve.
It is also possible to provide the at least one valve with at least one valving element which is designed to vary the rate of fluid flow between the first and second compartments in accordance with a memory effect.
It is equally possible to provide the at least one valve with at least one valving element which is movable in response to changes of at least one of the aforementioned plurality of parameters to thereby vary the rate of fluid flow between the first and second compartments independently of at least one of the first and second pressures. The at least one valve embodying such at least one valving element can include or constitute a slide valve.
The piston of the lockup clutch can be designed to include a radially inner portion having a first diameter and surrounding a central opening of the piston, and a radially outer portion having a second diameter larger than the first diameter. The at least one valve can be installed in such a way that it is nearer to the radially inner portion than to the radially outer portion of the piston.
The lockup clutch can further comprise a torsional vibration damper which operates between the piston and the output member of the turbine. The damper is or can be disposed at a first radial distance from the predetermined axis and the at least one valve is or can be disposed at a lesser or shorter second distance from the predetermined axis.
The torsional vibration damper can comprise one or more energy storing elements (e.g., coil springs acting in the circumferential direction of the turbine) disposed at a first radial distance from the predetermined axis, and the at least one valve is or can be disposed at a lesser second radial distance from such axis.
The piston of the lockup clutch can comprise an annular toothed radially inner portion disposed at a first radial distance from the predetermined axis, and the at least one valve can be installed at a second radial distance from the predetermined axis. The second distance is or can be selected in such a way that it at most matches but can be less than the first distance.
The at least one valve is or can be installed in the improved torque transmitting apparatus in such a way that it is adjacent a radially inner portion of the piston, and such radially inner portion of the piston is or can be spaced apart from the predetermined axis as seen in the radial direction of such axis.
As mentioned above, the prime mover can constitute or include or form part of an engine (e.g., a combustion engine) in a motor vehicle, and the output member can be designed to constitute or include or form part of a rotary input element of an adjustable transmission in the power train between the engine and one or more wheels of the motor vehicle. Such apparatus can further comprise a regulating unit which is designed to operate the torque converter and to adjust the transmission. Still further, such apparatus preferably comprises a source of hydraulic fluid including a pumping device which is controlled by the regulating unit and serves to supply hydraulic fluid to the adjustable transmission as well as to the lockup clutch. The regulating unit can comprise means for maintaining the lockup clutch in a disengaged condition when the temperature of fluid in the chamber of the torque converter is below a given value and for permitting engagement of the lockup clutch when the temperature of hydraulic fluid in the chamber of the torque converter rises above the given value. The at least one valve of such apparatus is preferably operative to establish the at least one path for the flow of fluid between the first and second compartments when the fluid temperature in the chamber is below the given value and to at least reduce the rate of fluid flow between the first and second compartments when the temperature of fluid in the chamber of the torque converter rises above the given value. The at least one valve of such apparatus can include, constitute or form part of a slide valve. The piston of the lockup clutch in such apparatus includes a radially inner portion which is spaced apart from the predetermined axis and the at least one valve can be installed adjacent the radially inner portion of such piston.
If the prime mover is an engine in a motor vehicle and the output member of the turbine constitutes or includes or forms part of the input element of an adjustable transmission, the apparatus preferably further comprises the aforementioned regulating unit which serves to operate the torque converter and to adjust the transmission, and the aforementioned source of hydraulic fluid which includes a pumping device controlled by the regulating unit to supply hydraulic fluid to the transmission and to the lockup clutch. In contrast to the aforementioned regulating unit, the regulating unit of the torque transmitting apparatus can include means for maintaining the lockup clutch in a disengaged condition when the temperature of fluid in the chamber of the torque converter is below a given value and for permitting engagement of the lockup clutch when the temperature of fluid in the chamber of the torque converter rises above the given value; the at least one valve of such apparatus is or can be operative to regulate the fluid flow between the first and second compartments as a function of changes of the temperature of fluid in the chamber of the torque converter. The at least one valve of such torque transmitting apparatus can include, constitute or form part of a slide valve.
The at least one valve of the improved torque transmitting apparatus can comprise at least one valving element which is movable between open and closed positions to thereby respectively permit the fluid to flow between the first and second compartments and to at least substantially prevent the fluid from flowing between the first and second compartments. Such at least one valve can further comprise means for moving the valving element at least from one of the open and closed positions to the other of these positions in stepwise fashion. Alternatively, the moving means of the at least one valve can be designed to gradually move the valving element at least from one of the open and closed positions toward the other of these positions.
The lockup clutch can further comprise at least one torsional vibration damper which operates between the piston of the clutch and the output member of the turbine. The damper can be installed at a first radial distance from the predetermined axis and the at least one valve can be installed at a lesser second radial distance from the predetermined axis. The at least one valving element of the at least one valve forming part of such torque transmitting apparatus can be installed for movement between open and closed positions and the at least one valve can further comprise means for gradually moving the valving element at least from one of the open and closed positions toward the other position in accordance with a predetermined program. Alternatively, the means for moving the at least one valving element from at least one of the open and closed positions toward the other position can be designed to abruptly move the at least one valving element to at least one of the open and closed positions.
As already mentioned hereinbefore, the piston of the lockup clutch can include a toothed radially inner portion disposed at a first radial distance from the predetermined axis and the at least one valve can be installed at a second radial distance from such axis. The second radial distance is preferably selected in such a way that it does not exceed but can be less than the first radial distance. The at least one valving element of the at least one valve in such torque transmitting apparatus is movable between open and at least substantially closed positions and the at least one valve preferably further comprises means for abruptly moving the at least one valving element to at least one of the open and at least partially closed positions.
The at least one valve can be provided with at least one opening (e.g., in the form of an elongated slot) which establishes the at least one path for the flow of hydraulic fluid between the first and second compartments, and such at least one valve can further comprise means for varying the rate of fluid flow through the at least one opening. The means for varying the rate of fluid flow can comprise means for regulating the rate of fluid flow through the at least one opening in accordance with a predetermined pattern.
The torque converter further comprises a housing which defines the aforementioned chamber, and the at least one valve is or can be installed in such housing.
The at least one valve is or can be connected with the piston of the torque converter. For example, the at least one valve can be mounted on the piston.
As already explained hereinbefore, the at least one valve can comprise at least one valving element which is movable between an open position to thus establish a flow of fluid between the first and second compartments in a first direction (e.g., in the direction of the predetermined axis) and a second position in which the at least one valving element at least reduces the rate of fluid flow between the first and second compartments. Such at least one valve can further comprise means for moving the at least one valving element from the second position in a direction at least substantialy at right angles to the first direction. Such means for moving the at least one valving element can include means for imparting to the at least one valving element a composite movement including a movement in the second direction at least during a first stage of movement from the second position and a movement in a third direction during a next-following stage of movement of the at least one valving element from the second position.
The means for moving the at least one valving element at least from one of the open and at least substantially closed positions toward the other position is preferably designed to move the at least one valving element at an angle to the direction of fluid flow between the two compartments in the open position of the at least one valving element. Such angle is or can be between about 300 and about 90xc2x0.
The construction of the at least one valve is or can be such that the at least one valving element is movable from at least one of the open and at least substantially closed positions toward the other of these positions in a direction substantially at right angles to the direction of flow of fluid between the first and second compartments in the open position of the at least one valving element, and such movement of the valving element in a direction substantially at right angles to the direction of fluid flow is or can be at least substantially independent of the fluid pressure in at least one of the first and second compartments. The at least one valve comprising such valving element or elements can include, form part or constitute a slide valve. Expressed in a somewhat different way, the at least one valving element is preferably movable from at least one of its positions toward the other position in a direction at an angle greater than 0xc2x0 to the direction of fluid flow between the first and second compartments in the open position of the at least one valving element.
Another feature of the invention resides in the provision of an apparatus for transmitting torque between a rotary output element (such as a crankshaft or a camshaft) of an engine (e.g., an internal combustion engine) in a motor vehicle and a rotary input element (e.g., a shaft) of an adjustable transmission between the engine and one or more wheels of the vehicle. The apparatus comprises a hydrokinetic torque converter including a pump which is driven by the output element of the engine and a turbine which is or which can be driven by the pump and serves to drive the input element of the transmission. The apparatus further comprises an engageable and disengageable lockup clutch or bypass clutch which is engageable to transmit torque from the output element of the engine to the turbine and/or to the input element of the transmission, a regulating unit which serves to operate the torque converter and to adjust the transmission, and a pumping device which is controlled by the regulating unit and serves to supply a hydraulic fluid (such as oil) to the transmission and to the clutch. The regulating unit includes means for maintaining the clutch in the disengaged condition when the fluid temperature in a chamber of the torque converter is below a given value and for permitting engagement of the clutch when the temperature of fluid in the chamber rises above the given value. Still further, the apparatus comprises at least one valve which is operative to establish and at least substantially seal a path between a first compartment and a second compartment at opposite sides of a mobile piston of the lockup clutch. The at least one valve includes at least one valving element which serves to establish the path for the flow of fluid between the first and second compartments when the fluid temperature in the chamber is below a given value and to at least reduce the rate of fluid flow between the first and second compartments when the temperature of fluid in the chamber rises above the given value. The at least one valve can be installed adjacent a radially inner portion of the piston forming part of the lockup clutch.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved torque transmitting apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.